The present invention relates generally to the working or forming of amorphous alloy materials which are difficult to work. More specifically, it relates to the cutting, slitting, rolling or stamping of amorphous alloys.
It is known that several working or forming operations performed on amorphous alloys such as cutting, slitting, rolling or stamping are operations which are difficult to perform when the material treated is at room temperature. The deformation of any material requires a flow of material as the material is formed or worked and at low temperatures the flow of amorphous alloys is governed by an inhomogeneous deformation mechanism. This deformation mechanism is characterized by high stresses and because of the high stresses the tools used in the forming operations have short useful lives. In addition, it is known that inhomogeneous deformation of amorphous alloys is detrimental to the soft magnetic properties of the alloys.
It has been known, heretofore, that some of the difficulties in forming the amorphous alloys can be overcome or reduced by performing the forming operations at elevated temperatures. This has been reported by Masumoto in Japanese patent application No. 132288, dated Nov. 5, 1976. In this publication, it is taught that forming processes should be applied to the amorphous alloy only at temperatures above the "ductile transition temperature" and this temperature is designated as T.sub.p. The same temperature which has been regarded as critical for working has also been referred to as the "plastic transition temperature" in an article by Liebermann, in Mat. Sci. Eng. 46, 241 (1980). It is known that above this plastic transition temperature the amorphous alloys can be deformed at low stresses to a high degree of straining. Patterson et al reported the hot forming of a metallic glass and demonstrated this hot forming by drawing a cup from a ribbon of amorphous alloy. This is reported in J. Patterson, A. L. Greer, J. A. Leake and D. R. H. in "Proceedings Third International Conference on Rapidly Quenched Metals", (Chameleon Press, 1978), p. 293.
More recently, Homer and Eberhardt produced strains approaching 100% in an amorphous alloy ribbon of PdFeSi at stresses as low as 150 Mpa by a deformation which was carried out at high temperatures. This was reported in Scripta Met. 14, 1331 (1980).
In none of the foregoing studies and methods developed from the studies was there any concern with the effect of the rate of heating of the article to be formed on the forming of the amorphous article. Primary consideration of this prior art work was the consideration of the crystallization kinetics of the alloy. An object was to effect the working without imparting significant degrees of crystallinity to the product. In this way it was sought to retain the amorphous character of the article which was being formed. The avoidance of crystallization is a primary consideration in preserving the properties of the amorphous alloys.
We have succeeded in discovering a relationship between the softening and increase in workability of an amorphous alloy article and the heating rate or the rate at which the article is undergoing heating. It is important to distinguish between the heating history of the article, that is the heating to a certain temperature prior to working or the rate at which an article has been heated to attain a certain temperature prior to working, and the effect which we have found to be important, namely the rate at which an article is being heated at the very time the working or forming of the article is taking place. We have found that an article such as an amorphous alloy undergoes a softening when and, more specifically, during the time when it is undergoing the heating at a relatively high heating rate. Further, we have succeeded in determining the variation of the softening temperature with or as a function of the heating rate in a quantitative manner.